JPH06109506A - Heating element type air flowmeter - Google Patents

Abstract

PURPOSE:To obtain a heating element type air flowmeter for automobile engine control system and the like from which a digital output signal can be acquired directly with high response along with air temperature information in the form of digital signal from a temperature compensation resistor. CONSTITUTION:A voltage comparator 3 makes a decision on the differential voltage of a bridge circuit G for detecting variation of the resistance of a heating element 1 arranged in an air passage and then controls the operation of an up/down counter 9. Output therefrom is fed through a D/A converter 10, a differential amplifier 11, and a transistor 12 to the bridge circuit G in order to perform constant temperature control of the heating element 1 while at the same time count of the up/down counter 9 is outputted as a digital flow rate signal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heating resistor type air flow meter used in, for example, an automobile engine control system.

[0002]

2. Description of the Related Art Conventionally, in an automobile engine control system, a heating resistor having a temperature dependent resistance characteristic and a temperature sensing resistor for temperature compensation are arranged in an intake passage of an engine to measure an intake air flow rate. The technology is widely used. This type of air flow meter, when the temperature (resistance value) of the heating resistor changes due to changes in the intake air flow rate, controls the heating resistor to supply a heating current that maintains a constant temperature difference with respect to the air temperature, This heating current is converted into a voltage and taken out as an air flow rate signal.

The air flow rate signal is generally taken out as a voltage-converted analog signal, amplified by a differential amplifier, converted into a digital signal by an A / D converter, and taken into an engine control unit (ECU). However, such signal conversion is described in, for example, Japanese Patent Laid-Open No. 61-284.
According to this method, the A / D signal conversion accuracy directly affects the measurement accuracy.

In view of the above, recently, there is a demand for directly extracting the air flow rate signal as a digital signal and outputting it to the ECU side. For example, as disclosed in Japanese Patent Laid-Open No. 62-55515, a constant heating current is started to be supplied to a heating resistor by a start pulse signal synchronized with engine rotation, and the heating resistor is heated to a specific temperature (resistance Value), the heating current is cut off, and the time from this energization to the interruption (digital data) is used as the measurement data of the air flow rate (the time from this energization to the interruption has a relationship that increases as the air flow rate increases). Technology is proposed.

[0005]

However, as described above, the supply of a constant heating current to the heating resistor is started by the start pulse signal, and the heating current is changed when the heating resistor reaches a specific temperature (resistance value). In the method of shutting off and using the time from energization to shutoff as measurement data of the air flow rate, since the heating current is a constant current, it takes time to raise the heating resistor to a specific temperature as the air flow rate increases. There are some points that need improvement in terms of responsiveness.

The present invention has been made in view of the above points, and its main purpose is to take out the output of a bridge circuit having a heating resistor for detecting an air flow rate directly as an air flow rate signal which is a digital signal and with good responsiveness. It is to provide an air flow meter that can. Another object of the present invention is to provide an air flow meter which can be used for temperature data other than the air flow rate measurement by taking out an air temperature signal for temperature compensation used in the air flow meter as a digital signal.

[0007]

The main object is to provide a heating resistor having temperature dependent resistance characteristics and a temperature compensating resistor in an air passage, and the heating resistor has a constant temperature difference with respect to the air temperature. In a heating resistor type air flow meter provided with a current control circuit for supplying and controlling a heating current for maintaining the above, a bridge circuit composed of the heating resistor, a temperature compensation resistor and a fixed resistor for current detection, and a bridge circuit The current control circuit includes a comparator for comparing the difference voltage at the midpoint and an up / down counter for increasing / decreasing the count by the output of the comparator, and outputs a digital signal of the up / down counter as an air flow rate signal and the current control circuit. Is configured to apply a voltage obtained by D / A converting the output value of the up / down counter to the bridge circuit to control the supply of the heating current. It is achieved by (a first means for solving problems of this).

Another object of the present invention is to vary the resistance value of the multi-stage resistor by selecting the resistors in which the temperature compensating resistors provided in the bridge circuit are connected in multiple stages and the number of connecting stages of these resistors by switching control. And a switching circuit to be controlled, and a temperature sensitive resistor for detecting an air temperature by passing a constant current is provided outside the bridge circuit, and an air temperature signal detected by the temperature sensitive resistor is converted into an A / D signal. While converting to a digital signal by the converter and outputting as temperature data,
This is achieved by setting the switching circuit so as to variably control the multistage resistance of the bridge circuit based on the digital signal (this is referred to as a second problem solving means).

[0009]

Operation of the first problem-solving means ... In the present problem-solving means, basically, a heating resistor having a temperature-dependent resistance characteristic and a temperature compensating resistor are used to heat the heating resistor. The air flow rate is measured based on the current value (the resistance value of the heating resistor is a predetermined value, in other words, the heating current value at which the temperature of the heating resistor maintains a constant temperature difference with respect to the air temperature).

The heating current supply control (constant temperature control of the heating resistor) is performed by a bridge circuit including a heating resistor and a temperature compensating resistor, a comparator, an up / down counter, a D / A converter, etc. Using.

That is, when the resistance value of the heating resistor changes due to the change in the air flow rate, the midpoint voltage (difference voltage) of the bridge circuit changes, and the output of the comparator is used to judge whether the midpoint voltage is positive or negative due to this change. The up / down counter controls the increase / decrease of the count by the output of this comparator. For example, if the resistance value of the heating resistor becomes smaller than a predetermined value due to an increase in the air flow rate, the comparator will output a high level, and while this high level continues, the up / down counter will count up, and conversely the air flow rate will decrease. When the resistance value of the heating resistor becomes larger than the predetermined value, the comparator outputs a low level, and the up / down counter counts down while the low level continues. in this way,
The output voltage (count value) of the up-down counter increases or decreases according to the change in the resistance value of the heating resistor due to the change in the air flow rate.
If / A is converted and applied to the bridge circuit, heating current control of the heating resistor (constant temperature control such that the temperature of the heating resistor reaches a specific temperature) is performed.

At the same time, the digital signal obtained by the up / down counter is output as an air flow rate signal to, for example, an engine control unit. Therefore, the air flow rate signal can be directly taken out as a digital signal from the bridge circuit through the comparator and the up / down counter.

Operation of Second Problem Solving Means ... In this problem solving means, the temperature-sensitive resistor provided outside the bridge circuit is also a temperature-dependent resistance element, and a constant current is passed through it to change the element voltage. By A / D conversion, the air temperature signal can be obtained as a digital signal, which can be used as data of various control devices, for example.

Also, this digital signal (air temperature signal)
Is input to the switching circuit of the temperature compensation resistance (multi-stage resistance) provided in the bridge circuit, and the switching circuit uses the digital signal to determine the resistance value of the multi-stage resistance of the bridge circuit and the temperature-sensitive resistance outside the bridge circuit (air temperature By variably controlling the resistance value corresponding to the (detection resistance), this multi-stage resistance functions as temperature compensation.

[0015]

Embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a circuit diagram of an intake air flowmeter of an automobile engine control system according to a first embodiment of the present invention.

In FIG. 1, the heating resistor 1, the current detecting resistor 2, the resistors 6 and 7 and the multistage variable resistor 8 constitute a bridge circuit G. The heating resistor 1 is used as an air flow rate measuring element and has a positive temperature coefficient as a temperature dependent characteristic. The multi-stage variable resistor 8 includes a temperature sensitive resistor (air temperature detecting resistor) 4, an A / D converter 13 and a switching circuit 1 which will be described later.
Used as a temperature compensation resistor in cooperation with No. The heating resistor 1 and the temperature sensitive resistor 4 are arranged in the intake air passage of the engine. The resistors 6 and 7 are for adjusting the offset voltage of the bridge circuit.

Here, the multistage variable resistor 8, the temperature sensitive resistor 4,
The A / D converter 13 and the switching circuit 15 will be described.

The multi-stage variable resistor 8 is provided on one side of the bridge circuit G, while the temperature sensitive resistor 4 serving as an air temperature detecting resistor is connected outside the bridge circuit G (lower stage of the bridge circuit G). A constant current is supplied to the temperature sensitive resistor 4 by using a constant current power source 14, the detected voltage of the temperature sensitive resistor 4 is converted into a digital signal by the A / D converter 13, and the parallel air temperature signal D _T is obtained. The temperature data is output to an ECU (engine control unit; microcomputer) (not shown) via the terminal 33. This air temperature signal D _T is used on the ECU side for computer coefficient correction, for example. In order to take out the temperature data D _T as a highly accurate digital signal, the temperature data D _T is removed from the bridge circuit G and connected to the constant current source 14.

The digital signal output from the A / D converter 13 is input to the switching circuit 15. The switching circuit 15 has a function of variably controlling the resistance value of the multistage resistor 8 by selecting the connection stage number of the multistage resistor 8 by switching control based on the digital signal from the A / D converter 13. The variable control of the multi-stage resistor 8 is controlled so as to be a value corresponding to the resistance value of the temperature sensitive resistance element 4 based on the air temperature signal D _T (digital signal).

The voltage at one of the midpoints of the bridge circuit G (the midpoint between the heating resistor 1 and the current detection resistor 2) is input to the non-inverting input terminal of a voltage comparator (hereinafter referred to as comparator) 3. , Other (multi-stage variable resistor 8, midpoint between resistors 7 and 6)
Is input to the inverting input terminal of the comparator 3, and the up / down counter 9 performs an increase / decrease counting operation based on the output of the comparator 3.

That is, when the resistance value of the heating resistor 1 changes due to the change of the intake air flow rate, the midpoint voltage (difference voltage) of the bridge circuit G changes, and the positive / negative discrimination of the midpoint voltage due to this change is compared. The output of the comparator 3 is performed, and the output of the comparator 3 controls the up / down counter 9 to increase / decrease the count. For example, when the resistance value of the heating resistor 1 decreases due to an increase in the air flow rate, the midpoint voltage between the heating resistor 1 and the resistor 2 increases, and the comparison voltage (the difference between the non-inverting input terminal and the inverting input terminal of the comparator 3) is increased. ) Becomes positive, the comparator 3 becomes a high level output, and while this high level continues, the up / down counter is counted up, and conversely, when the resistance value of the heating resistor 1 becomes larger than a predetermined value due to the decrease of the air flow rate. The comparator outputs low level, and the up / down counter 9 counts down while the low level continues. Thus, the output voltage (count value) of the up / down counter 9 increases / decreases due to the change in the resistance value of the heating resistor 1 accompanying the change in the air flow rate.

The digital output D _Q of the up / down counter 9 is converted into an analog voltage by the D / A converter 10 and applied to the base of the current control power transistor 12 via the differential amplifier 11. That is, the differential amplifier 11 has an analog signal from the D / A converter 10 at one of its input terminals and a midpoint voltage of one of the bridge circuits (intermediate between the resistors 7 and 6) at the other input terminal. (Point voltage) is input, the difference voltage is amplified and applied to the power transistor 12, and the heating current flowing through the heating resistor 1 of the bridge circuit G is controlled. The heating current control of the heating resistor 1 is a constant temperature control such that the temperature of the heating resistor 1 becomes a specific temperature.

Since the digital output of the up / down counter 9 changes according to the air flow rate, it is output to the ECU as parallel data via the latch circuit 24 and the terminal 28 as an air flow rate signal D _Q.

The clock circuit 23 outputs a clock signal for driving the up / down counter 9, the latch circuit 24 and the flip-flop circuit 26, and the flip-flop circuit 26 receives the timing signal T input from the terminal 29.
Based on the above, the air flow rate signal D _Q is rewritten using the latch 24, and the latched air flow rate signal (parallel data)
D _Q is sent to the outside (ECU).

Reference numeral 17 is a voltage dividing resistor for extracting the midpoint voltage of the bridge circuit G (voltage between the heating resistor 1 and the current detecting resistor 2), and the reference power source 16 and the resistor 18 are the input voltage of the comparator 3. It is for giving a hysteresis characteristic and has a function of stabilizing the output of the comparator 3 and stabilizing the air flow rate signal. 19, 20, 21 are voltage dividing resistors, 30 is a ground terminal, 32 is an A / D converter 13 Is a clock terminal for driving the power source, and V _B is a power input terminal.

According to the present embodiment, the midpoint voltage of the bridge circuit G can be directly taken out as a digital air flow rate signal through the comparator 3 and the up / down counter 9 with good responsiveness, and the temperature sensing resistor 4 can be used. The detected value can be given to the outside as air temperature data of a highly accurate digital signal.

FIG. 2 shows a second embodiment of the present invention.
The same reference numerals as those in the first embodiment indicate the same or common elements (the same applies to FIG. 3 and subsequent figures).

The present embodiment differs from the first embodiment in that a modem 25 and a serial data output terminal 31 are provided in place of the latch circuit 24 and the parallel data output terminals 28 and 33 shown in FIG. .

According to the present embodiment, the air flow rate signal (digital signal) D _Q from the up / down counter 9 and the air temperature signal (digital signal) D _T from the A / D converter 13 are serialized by the modem 25. Can be converted into the output signal and output by the terminal 31. In this case, the output signals D _Q and D _T from the modem 25 are alternately switched based on the timing signal T. According to the present embodiment, by adopting serial data transmission, there is an advantage that the air flow rate signal and the air temperature signal are transmitted by one signal line.

FIG. 3 shows a third embodiment of the present invention, which is different from the second embodiment in that the data select circuit 3 is provided in addition to the modem 25.
4 is provided, and both parallel data and serial data are used for data transmission. The parallel data of the air flow rate signal D _Q and the air temperature signal D _{T, which} are digital signals, are configured so that they can be output from one parallel output terminal 35. In this case, the timing signal T of the terminal 29 input from the outside is input. Then, the output of the data selector 34 is switched to the air flow rate signal D _Q and the air temperature signal D _T for output. The serial transmission by the modem 25 is the same as in the second embodiment.

According to this embodiment, there is an advantage that the air flow rate signal D _Q and the air temperature signal D _T can be output as digital signals by one parallel output terminal 35.

FIG. 4 shows a fourth embodiment of the present invention, in which the midpoint voltage of the bridge circuit G is directly taken out as a digital signal via the comparator 3 and the up / down counter 9 as in the above embodiments. However, the means for taking out the air temperature signal D _T digitally is omitted, and the temperature sensitive resistor 4 is directly incorporated in the bridge circuit G. In this way, the air flow rate signal D _Q
Only the signal is output as a digital signal.

[0034]

According to the first means for solving the problems, by connecting the comparator to the middle point of the bridge circuit composed of the heating resistor, the temperature compensating resistor, etc., and the up / down counter at the subsequent stage, The air flow rate signal can be directly taken out as a digital signal from the bridge circuit. as a result,
It is possible to output a highly accurate air flow rate signal as a digital signal without being affected by the A / D conversion accuracy as in the past.
Further, it is possible to obtain noise-resistant air flow rate measurement data. Even when the air flow rate signal is directly taken out as a digital signal from the bridge circuit in this way, the heating current of the bridge circuit can be increased according to the air flow rate instead of the constant current. It is possible to shorten the time required to bring the body to a specific temperature and improve the responsiveness of the air flow rate measurement.

According to the second means for solving problems, the temperature-compensating air temperature signal used in the air flow meter can be taken out as a digital signal and used for temperature data other than the air flow rate measurement.

[Brief description of drawings]

FIG. 1 is a circuit configuration diagram according to a first embodiment of the present invention.

FIG. 2 is a circuit configuration diagram according to a second embodiment of the present invention.

FIG. 3 is a circuit configuration diagram according to a third embodiment of the present invention.

FIG. 4 is a circuit configuration diagram according to a fourth embodiment of the present invention.

[Explanation of symbols]

G ... Bridge circuit, 1 ... Heating resistor, 3 ... Comparator, 4 ...
Temperature-sensitive resistor (air temperature detection resistor), 8 ... Multi-stage variable resistor,
9 ... Up-down counter, 10 ... D / A converter, 11
... differential amplifier, 13 ... D / A converter, 15 ... switching circuit, 25 ... modem, 28, 33 ... parallel data terminal, 31 ... serial data terminal, 34 ... data select circuit.

Claims (4)

[Claims] 1. A heating resistor having a temperature-dependent resistance characteristic and a temperature compensating resistor are arranged in an air passage, and a heating current for maintaining a constant temperature difference with respect to the air temperature is supplied to the heating resistor to control the heating current. In a heating resistor type air flow meter equipped with a current control circuit, a bridge circuit composed of the heating resistor, a temperature compensating resistor and a fixed resistor for current detection is compared with a difference voltage at a middle point of the bridge circuit. A comparator and an up / down counter for increasing / decreasing the count by the output of the comparator are provided, and the current control circuit outputs the digital signal of the up / down counter as an air flow rate signal and the output of the up / down counter. A heating resistor type characterized in that a voltage obtained by D / A converting the value is applied to the bridge circuit to control the supply of the heating current. Air flow rate meter. 2. The temperature compensating resistor provided in the bridge circuit according to claim 1, wherein the resistors connected in multiple stages and the number of connected stages of these resistors are selected by switching control to change the resistance value of the multistage resistors. A temperature sensitive resistor, which is composed of a switching circuit for controlling, is provided outside the bridge circuit to detect an air temperature by passing a constant current, and an air temperature signal detected by the temperature sensitive resistor is converted into an A / D signal. A heating resistor type air flow meter, characterized in that a converter converts it into a digital signal and outputs it as temperature data, and the switching circuit variably controls the multistage resistance of the bridge circuit based on the digital signal. . 3. The air flow rate signal and the air temperature signal according to claim 2, wherein the air flow rate signal and the air temperature signal are output as digital signals from the same output terminal, and data acquisition of these signals can be selected by an external signal input. An air flow meter with a heating resistor. 4. The device according to claim 3, further comprising means for converting the air flow rate signal and the air temperature signal obtained as parallel data into serial data, and the acquisition of these serial data can be selected by an input signal from the outside. A heating resistor type air flow meter characterized in that.